During the joint welding of rotor shafts in turbine and generator construction, so-called narrow-gap arc welding technology is used to assemble forged shaft parts to form a complete rotor.
With known methods, if it is intended to provide more than two joints per rotor, the rotor portions are stacked one on top of each other in a vertical axis arrangement and welded together in two steps. Here, the welding of the first beads, so-called root welding, is performed using the so-called narrow-gap tungsten inert gas (TIG) method. After root welding of all joints, the rotor is tilted from the vertical axis position into the horizontal axis position and the remaining seam cross section welded in this position according to the so-called narrow-gap submerged arc welding method (SAW).
The required joint cross section, i.e. the bead thickness of the root weld, results from the requirement for the partially welded rotor to have sufficient mechanical strength for the tilting process. Depending upon the partial rotor mass ratios, the usual TIG bead thicknesses lie between about 20 mm and 30 mm. The tilting is necessary to enable the remaining seam cross section to be welded more quickly and economically using the high-performance SAW method. The root-welded rotor has to be tilted because the SAW method cannot be used efficiently with a horizontal position of the rotor axis. In addition, with certain rotor materials, an additional heat supply is required to prevent cracking due to the tilting.